Aggregation induced emission dynamic chiral europium(III) complexes with excellent circularly polarized luminescence and smart sensors

The synthesis of dynamic chiral lanthanide complex emitters has always been difficult. Herein, we report three pairs of dynamic chiral EuIII complex emitters (R/S-Eu-R-1, R = Et/Me; R/S-Eu-Et-2) with aggregation-induced emission. In the molecular state, these EuIII complexes have almost no obvious emission, while in the aggregate state, they greatly enhance the EuIII emission through restriction of intramolecular rotation and restriction of intramolecular vibration. The asymmetry factor and the circularly polarized luminescence brightness are as high as 0.64 (5D0 → 7F1) and 2429 M−1cm−1 of R-Eu-Et-1, achieving a rare double improvement. R-Eu-Et-1/2 exhibit excellent sensing properties for low concentrations of CuII ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively. Dynamic EuIII complexes are constructed by using chiral ligands with rotor structures or vibration units, an approach that opens a door for the construction of dynamic chiral luminescent materials.


Aggregation induced emission dynamic chiral europium(III) complexes with excellent circularly polarized luminescence and smart sensors
Yun-Lan Li 1 , Hai-Ling Wang 1 , Zhong-Hong Zhu 1 , Yu-Feng Wang 1 , Fu-Pei Liang 1 & Hua-Hong Zou 1 The synthesis of dynamic chiral lanthanide complex emitters has always been difficult.Herein, we report three pairs of dynamic chiral Eu III complex emitters (R/S-Eu-R-1, R = Et/Me; R/S-Eu-Et-2) with aggregation-induced emission.In the molecular state, these Eu III complexes have almost no obvious emission, while in the aggregate state, they greatly enhance the Eu III emission through restriction of intramolecular rotation and restriction of intramolecular vibration.The asymmetry factor and the circularly polarized luminescence brightness are as high as 0.64 ( 5 D 0 → 7 F 1 ) and 2429 M −1 cm −1 of R-Eu-Et-1, achieving a rare double improvement.R-Eu-Et-1/2 exhibit excellent sensing properties for low concentrations of Cu II ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively.Dynamic Eu III complexes are constructed by using chiral ligands with rotor structures or vibration units, an approach that opens a door for the construction of dynamic chiral luminescent materials.
Lanthanide complex emitters with many advantages such as narrow emission peak, good monochromaticity, large Stokes shift, long excited state lifetime, and strong light absorption ability have attracted great attention [1][2][3][4] .The complex electronic configuration of the 4 f n electron shell of trivalent lanthanide metal ions lead to electron excitation to the high-energy 4f orbital which is hardly affected by the ligands in complexes.Therefore, lanthanide complex emitters have bright and clear emission lines 5,6 .Rational construction of lanthanide complex emitters with excellent luminescent properties has promoted the rapid development of smart sensing, solid-state lighting, anticounterfeiting, and biodiagnostics [7][8][9][10] .The short triplet lifetimes of most organic ligands and their poor energy-level matching with lanthanide ions hinder the efficient construction of lanthanide complex emitters 11,12 .Although a variety of organic ligands have been synthesized to act as antennas to solve the above problems, the energy levels of organic ligands with specific structures and fixed configurations are precise, and effectively constructing dynamic lanthanide complex emitters is impossible 13,14 .Therefore, reconsidering the method of synthesizing lanthanide complexes with efficient dynamic luminescence properties is urgently needed.
In 2001, Tang et al. discovered that the fluorescence of organic fluorophores with a molecular rotor structure gradually rises with the increase of the degree of aggregation, and they proposed aggregationinduced emission (AIE) 15 .Currently, restriction of intramolecular motion (RIM) is the most recognized mechanism for constructing efficient and bright AIE fluorophores (AIEgens), and this method can be further divided into the restriction of intramolecular rotation (RIR) and restriction of intramolecular vibration (RIV) mechanisms 16,17 .In recent years, some dynamic luminescent complexes which rely on the RIM mechanism and exhibit AIE behavior have gradually appeared and have shown attractive application prospects in the fields of intelligent sensing, multiple anti-counterfeiting, solid-state lighting, circularly polarized luminescence, and biological diagnosis and treatment [18][19][20][21][22] .In 2020, Zang et al. used the chiral ligand (R/S)−2,2'-bis(di-p-tolylphosphine)−1,1'-binaphthalene to coordinate with the Cu I ion to obtain a pair of chiral Cu I complex isomers which show photoresponse performance and circularly polarized luminescence (CPL) performance 23 .Next, the research group used a butterfly-like organic ligand oxacalix [2]arene [2]pyrazine to construct a dynamic luminescent metal-organic framework (MOF) with RIV properties through a simple solvothermal reaction 24 .Although some progress has been made in the rational design and synthesis of dynamic luminescent MOFs and transition metal complex emitters, the construction of dynamic lanthanide complex emitters has not yet been realized.Selecting organic ligands with obvious molecular rotor structures or vibrational units which match the energy levels of Ln III ions is one of the most effective ways to rationally construct dynamic lanthanide complex emitters.
In recent years, chiral complex emitters have become a research hotspot and have potential applications in the fields of nonlinear optics, anti-counterfeiting inks, three-dimensional displays, and polarized light microscopy [25][26][27][28][29] .Thus far, achieving both high luminescence asymmetry factor (g lum ) and circularly polarized luminescence brightness (B CPL ) is difficult for most chiral luminescent materials 30 .High B CPL values can depend on molecules with excellent molar absorptivity, but their relatively low g lum ; however, unusually strong g lum can be hampered by weak molar absorptivity and quantum yield (QY), resulting in unsatisfactory B CPL values.Chiral lanthanide complexes usually exhibit high g lum values given the magnetic dipole-allowed transitions of lanthanide metal ions [31][32][33] .In addition, the characteristic radiative transitions of lanthanide emitters can be promoted by enhancing the antenna effect to obtain high QY [34][35][36] .Therefore, chiral lanthanide complex emitters are one of the best candidates for constructing CPL materials with high-performance parameters, and they are expected to achieve double improvement in g lum and B CPL values.
Heavy metal ion pollution has become a serious environmental problem.Such pollutants often exist in industrial wastewater and cannot be degraded by organisms, eventually entering the food chain system, and seriously threatening human health and the balance of natural ecosystems.Especially for the heavy metal ion Cu II , excessive absorption by plants can cause physiological metabolic disorders, and growth and development retardation poisoning; further, a large amount of Cu II can combine with albumin in serum to cause damage to the liver and central nervous system 37,38 .The United States Environmental Protection Agency (USEPA) prescribes that the maximum permission concentration of Cu II ions in drinking water cannot exceed 20 μM 14 .Sensitivity is one of the most important metrics for measuring high-performance sensors 39,40 .Therefore, the development of highly sensitive sensors capable of fast and intelligent responses to very low concentrations of Cu II ions is of great importance.
Herein, we used chiral organic ligands with molecular rotor structures or vibrational units to react with lanthanide metal ions under solvothermal conditions and obtained three pairs of dynamic chiral Eu III complex isomers with RIM characteristics (R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2).The simple, efficient, high-yield, and atomutilizing solvothermal one-pot method effectively avoids the complicated organic synthesis process and provides a strategy for the rational construction of dynamic lanthanide complex emitters.Note that with the gradual increase of glycerin, the emission intensity of the four chiral Eu III complex emitters increases significantly, showing α AIE values as high as 92.54/87.95(R/S-Eu-Et-1), and 13.44/16.8(R/S-Eu-Et-2).In addition, the chiral Eu III complex R-Eu-Et-1 has both high g lum (0.64) and B CPL (2429 M −1 cm −1 ), realizing the double improvement of CPL parameters.Both R-Eu-Et-1/2 in the aggregated state exhibit highly sensitive photoresponses to very low concentrations of Cu II ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively, much lower than the maximum permissible value (20 μM) of Cu II ion in drinking water stipulated by USEPA.High-resolution electrospray mass spectrometry (HRESI-MS) results demonstrate that Cu II ions replace Ln III ions in the chiral lanthanide complex emitters to induce strong ligand-to-metal charge transfer (LMCT) leading to luminescence quenching.Furthermore, R-Eu-Et-1 exhibits excellent photoresponses to both low-concentration acidic and alkaline aqueous solutions.This work synthesized a series of chiral dynamic lanthanide complex emitters and developed a strategy for the rational design and construction of dynamic lanthanide complex emitters (Fig. 1).In addition, this research provides a perspective for the design and synthesis of metal complex emitters with CPL performance and multiple sensing.

Results
Crystal structural analysis of R/S-Eu-R-1 (R = Et/Me), R/S-Eu-Et-2, and Eu-Et-3 Accurately weighed (1 R/S,2 R/S)-(-/ + )−1,2-diphenylethylenediamine, 1-methyl/ethyl-2-imidazolecarboxaldehyde, and Eu(NO 3 ) 3 •6H 2 O with a stoichiometric ratio of 1:1:1 were dissolved in a mixed solvent of EtOH and CH 3 CN (1:1) and underwent a solvothermal reaction under one-pot conditions, an approach which easily and quickly generated two pairs of chiral Eu III complexes R/S-Eu-R-1 (R = Et/Me) containing molecular rotor structures in high yield.The one-pot synthesis strategy under solvothermal conditions effectively avoids tedious organic synthesis, improves atom utilization, and reduces cost and time.Single crystal X-ray diffraction (SCXRD) results show that R/S-Eu-R-1 is crystallized in the orthorhombic chiral space group P2 1 2 1 2 1 (Supplementary Table 1).R/S-Eu-R-1 (R = Et/Me) are enantiomers of each other, and they have similar structural connections (Supplementary Fig. 1A).As shown in Figs.2A, R ) with multidentate chelate coordination and molecular rotors, and the combination of three end-group coordinated NO 3 − ions, and its molecular formula is [Eu(R-L 1 )(NO 3 ) 3 ].In the molecular state, the ligand R-L 1 in the structure of R-Eu-Et-1 has two molecular rotors that can rotate freely.In the aggregated state, the molecular rotors between two adjacent R-Eu-Et-1 molecules crossstack each other and greatly restrict the free rotation of the benzene ring rotors through strong hydrogen bonds and steric hindrance (Fig. 2B).In addition, R-Eu-Et-1 in the aggregated state is connected by five different strong hydrogen bonds C-H • • • O bonds to form a threedimensional structure (Fig. 2C).First, hydrogen bond I (C 50 -H Note that a strong hydrogen bond (II-V) exists between the hydrogen atom on the molecular rotor and the hydrogen bond acceptor oxygen atom on the nitrate, and this bond fixes the molecular conformation of R-Eu-Et-1 and locks the molecular rotor.The introduction of a molecular rotor structure can help facilitate the construction of artificial intelligence molecules, and as far as we know, artificial intelligence molecules based on lanthanide complexes are very rare.Structural analysis shows that the Eu III ion in the R-Eu-Et-1 structure is in the O 6 N 4 coordination environment jointly provided by R-L 1 and NO 3 − .SHAPE calculates that the coordination configuration of the above Eu III ion is sphenocorona with a C 2v symmetric environment (Supplementary Fig. 1D and Supplementary Table 2).In the R-Eu-Et-1 structure, the coordination mode of the ligand R-L 1 is as follows: μ 1ƞ 1 :ƞ 1 :ƞ 1 :ƞ 1 (Supplementary Fig. 1B).Topological analysis shows that R-Eu-Et-1 can serve as an eight-connected fcu network with a distance ranging from 10.701 to 14.482 Å (Fig. 2D).All Ln−O/N bond lengths are within the normal range (Supplementary Data 1).
A pair of enantiomers R/S-Eu-Et-2 was obtained under the same reaction conditions by replacing (1 R/S,2 R/S)-(-/+)-cyclohexanediamine with an equimolar ratio of (1 R/S,2 R/S)-(-/ + )−1,2-diphenylethylenediamine (Supplementary Fig. 1A and Data 1).SCXRD indicates that R/S-Eu-Et-2 crystallizes in the orthorhombic space group P2 1 2 1 2 1 (Supplementary Table 1).As shown in Fig. 2E, R/S-Eu-Et-2 consists of an Eu III ion, a chiral Schiff base ligand (1E,1'E)-N,N'-(cyclohexane-1,2-diyl)bis(1-(1-ethyl-1H-imidazol-2-yl)methanimine) (R-L 2 ) with multidentate chelating coordination, three terminally coordinated NO 3 − ions, and a free CH 3 CN molecule, and its molecular formula is [Eu(R-L 2 )(NO 3 ) 3 ]CH 3 CN.Interestingly, in the molecular state of R-Eu-Et-2, the cyclohexane on R-L 2 exhibits intense vibration because of the configuration change.However, in the aggregated state, the configuration switching of cyclohexane in R-Eu-Et-2 is hindered by the −CH 2 CH 3 of R-L 2 and the oxygen atoms of NO 3 − on the adjacent molecule, making it difficult to effectively vibrate (Fig. 2F).R-Eu-Et-2 in the aggregated state consists of four kinds of C-H • • • O strong hydrogen bonds to form a three-dimensional structure (Fig. 2G).First, it forms a chain structure by linking multiple independent units through hydrogen bond VI (C 8 -H 8B In addition, the hydrogen atom on the R-L 2 ligand forms a C-H • • • N hydrogen bond (X, 3.945 Å) with the hydrogen bond acceptor nitrogen atom on the CH 3 CN.Notably, the hydrogen atoms on the cyclohexane vibration unit have strong hydrogen bond interactions with the hydrogen bond acceptor oxygen atoms on the nitrate (VI, VIII, and IX), a feature which helps to fix the R-Eu-Et-2 molecular conformation and lock the molecular vibration.To the best of our knowledge, this work constructs dynamic rare earth complexes based on molecular vibrations.Structural analysis shows that the Eu III ion in the R-Eu-Et-2 structure is in the O 6 N 4 coordination environment jointly provided by R-L 2 and NO 3 − .The coordination configuration of the Eu III ions and the coordination mode of the ligand (R-L 2 ) of R-Eu-Et-2 are consistent with those of R-Eu-Et-1 (Supplementary Fig. 1E and Table 3).In the R-Eu-Et-2 structure, the coordination mode of the ligand R-L 2 is as follows: μ 1 -ƞ 1 :ƞ 1 :ƞ 1 :ƞ 1 (Supplementary Fig. 1C).Topological analysis shows that R-Eu-Et-2 can serve as a six-connected fcu network with a distance ranging from 10.480 to 14.286 Å (Fig. 2H).(1 R,2 R)-(-)−1,2-diphenylethylenediamine was changed to ethylenediamine, and under the same synthesis conditions, a Eu III complex Eu-Et-3 was successfully obtained which does not have a rotor and vibrational primitives and has the same coordination environment as R-Et-Eu-1 (Supplementary Fig. 2).SCXRD results show that Eu-Et-3 crystallizes in the P -1 space group of the triclinic system (Supplementary Table 1).As shown in Supplementary Fig. 2A − ions.SHAPE calculated that the coordination configuration of the above Eu III ion is tetradecahedron with C 2v symmetry environment (Supplementary Fig. 2E and Table 4).In the Eu-Et-3 structure, the coordination mode of ligand L 3 is: μ 1 -ƞ 1 :ƞ 1 :ƞ 1 :ƞ 1 (Supplementary Fig. 2D).Topological analysis shows that Eu-Et-3 can be regarded as an eight-connected fcu network with a distance range of 7.859 to 10.844 Å (Supplementary Fig. 2F).

A. Restriction of Intramolecular Rotation
R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2, which are enantiomers, have same Fourier transform infrared (FTIR) characteristic absorption peaks at the similar position (Supplementary Fig. 3).Thermal stability tests of R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 were carried out under a flowing nitrogen atmosphere at a rate of 5 °Cmin −1 slowly ramped up from 35 °C to 1000 °C (Supplementary Fig. 4).All the experimental results show that R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 have excellent thermal stability.The SEM images of R/S-Eu-Me-1, R/S-Eu-Et-1, and R/S-Eu-Et-2 clearly show that they are all bulk crystals, and the surfaces are very clean (Supplementary Fig. 5).In addition, R/S-Eu-R-1 and R/S-Eu-Et-2 have similar polycrystalline powder X-ray diffraction (PXRD) spectra, indicating that they are pure phases (Supplementary Fig. 6).

Aggregation-induced Emission of R/S-Eu
A variety of AIEgens, AIEgens-based MOFs, and clusters with AIE behavior have been designed and synthesized in recent years, and they have shown broad application prospects in the fields of sensing, multiple anti-counterfeiting, solid-state lighting, and biological diagnosis and treatment [41][42][43][44] .At present, molecules with AIE properties are mainly designed and constructed based on restricted RIM, and the common strategy involves introducing structural units that can rotate or vibrate freely.According to the structural characteristics of R-Eu-Et-1/2, further studies were conducted on their AIE properties.Specifically, by using glycerin as a poor solvent, the same mass of R/S-Eu-Et-1 and R/S-Eu-Et-2 were dissolved in glycerin/DMSO mixed solutions with different glycerin contents (f w ), and their emission spectra were tested.The experimental results showed that with the increase of DMSO, the emission intensity of R/S-Eu-Et-1 and R/S-Eu-Et-2 gradually weakened.Moreover, with the increase of the content of glycerin, the emission intensity of the solution increases gradually, and strong luminescence was observed when the content of glycerin was 99%, indicating that both R/S-Eu-Et-1 and R/S-Eu-Et-2 have typical AIE characteristics (Fig. 3).Calculated by I/I 0 , the α AIE values of R/S-Eu-Et-1 and R/S-Eu-Et-2 are 92.54/87.95and 13.44/16.8(Fig. 3).To further verify the AIE behavior of R/S-Eu-Et-1, R/S-Eu-Et-2, and R/S-Eu-Me-1, we tested the QYs of R/S-Eu-Et-1 and R/S-Eu-Et-2, and R/S-Eu-Me-1 in glycerin/DMSO or CH 3 CN/DMF mixed solutions with different ratios.Experimental results show that as the proportion of poor solvent glycerin or CH 3 CN continues to increase, the luminescence QY of these Eu III complexes continues to increase.When the glycerin or CH 3 CN content is 99%, the  QYs of R/S-Eu-Et-1 and R/S-Eu-Et-2, and R/S-Eu-Me-1 reach the maximum, which are 27.2/27.9,27.8/24.1,25.0/28.0,26.3/26.7,18.6/19.9,and 29.5/29.9,respectively, once again proving that they have significant aggregation promotes antenna effect behavior (Supplementary Fig. 7−9 and Data 2).In addition, only the metal center Eu III ion was replaced by Tb III /Gd III ion and the isostructural R/S-Gd-Et-1, R/S-Gd-Me-1, R-Gd-Et-2, R-Tb-Et-1, R/S-Tb-Me-1, R-Tb-Et-2 were obtained respectively under the same conditions as R-Eu-Et-1 (Supplementary Table 1 and Fig. 10).Since the energy levels of R-L 1 and R-L 2 do not match the energy levels of Tb III /Gd III ions and the antenna effect cannot be performed, R/S-Gd-Et-1, R/S-Tb-Et-1, R/S-Gd-Et-2, R/S-Tb-Et-2, R-Gd-Me-1, R-Tb-Me-1 all exhibit fluorescence of the ligands.The emission spectra of the above lanthanide complexes were tested in mixed solutions of glycerin/DMSO with different ratios (f w ).The results show that R/S-Gd-Et-1, R/S-Tb-Et-1, R/S-Gd-Et-2, R/S-Tb-Et-2, R-Gd-Me-1, R-Tb-Me-1 and all exhibit obvious AIE behaviors (Supplementary Fig. 11−13).Meanwhile, we investigated the AIE properties of R/S-Eu-Me-1, and S-Eu-Et-1/2 in CH 3 CN/DMF mixtures by using CH 3 CN as a poor solvent.The experimental results show that the emission intensity of R/S-Eu-Me-1, and S-Eu-Et-1/2 is very weak in pure DMF solution (Supplementary Fig. 14 and 15).In the mixed solution with glycerin content of 99%, the UV-Vis absorption spectra of R/S-Eu-Et-1 and R/S-Eu-Et-2 obviously do not start from the origin but have a certain absorption value (Fig. 3C, F, I, L), which shows that they have formed an aggregated suspension in glycerin, and the above absorption value is given by aggregate scattering results.In addition, the UV-Vis absorption of R/S-Eu-Me-1 and S-Eu-Et-1/2 has a certain degree of red shift, which can be attributed to the size change of the complexes in the aggregated and dispersed states 24,[45][46][47] .R/S-Gd-Et-1, R/S-Gd-Et-2, R/S-Tb-Et-1, S-Eu-Et-1/2, and R/S-Eu-Me-1 have the same result (Supplementary Fig. 11, 12, 14, 15).The particle sizes of the aggregate's R/S-Eu-Et-1 and R/S-Eu-Et-2 in glycerin were measured by dynamic light scattering as 82/122 and 85/141 nm, respectively (Fig. 3C, F, I, L illustrations).In addition, the particle sizes of the aggregate's R/S-Eu-Me-1 and S-Eu-Et-1/2 in CH 3 CN were measured by dynamic light scattering as 712/615, and 390/396 nm, respectively (Supplementary Fig. 14, 15 illustrations).In addition, the Zeta potentials of R/S-Eu-Et-1, R/S-Eu-Et-2, and R/S-Eu-Me-1 in the aggregated state are -21.4/-24.23,-16.93/-20.13,and -21.63/-21.06mV, respectively, indicating that their aggregates can remain stable (Supplementary Fig. 16).Using CH 3 CN as a poor solvent, Eu-Et-3 was dissolved in CH 3 CN/DMF mixed solutions with different CH 3 CN contents (f w ), and the emission spectra of the above solutions were tested.Experimental results show that as the proportion of CH 3 CN increases, the emission intensity of Eu-Et-3 rapidly weakens, indicating that Eu-Et-3 has an ACQ effect (Supplementary Fig. 17).Furthermore, when we excited R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 dispersed in CH 3 CN solution with light at 365 nm, they both showed 592, 617, 650, and 685 nm, which are assigned to the 5 5 D 0 → 7 F 3 , and 5 D 0 → 7 F 4 energy level transitions of Eu III ions, respectively (Supplementary Fig. 18).The luminescence lifetimes of R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 dispersed in CH 3 CN are as long as τ 1/e = 1207.5 ( ± 0.022), 1225.9 ( ± 0.027), 1223.6 ( ± 0.031), 1246.4 ( ± 0.028), 1240.8 ( ± 0.047), and 1237.5 ( ± 0.023) μs (Supplementary Fig. 19).The QYs of R/S-Eu-R-1 and R/S-Eu-Et-2 dispersed in CH 3 CN are 26%/26% (R = Et), 29%/28% (R = Me), and 17%/17%, respectively (Supplementary Fig. 20).
The AIE properties of R-Eu-Et-1 can be explained by the RIR mechanism.In the single-molecule state, the ligand R-L 1 in the structure R-Eu-Et-1 has two molecular rotors that can rotate freely, so the excited state molecules mainly return to the ground state through nonradiative transitions, which leads to the shutdown of the ISC process and the ineffective ET process.Thus, the radiative transition channel of the lanthanide metal ion is closed.In the aggregated state, the rotation of the R-Eu-Et-1 molecular rotor is greatly restricted by the steric hindrance of adjacent molecules and strong hydrogen bonding, thereby closing the non-radiative transition channel of the excited state, opening the ISC process, and undertaking the ET process (antenna effect) to facilitate the radiative transition of lanthanide metal ions, consequently showing the characteristic emission of Eu III ions.This work marks that aggregation-enhanced antenna effects promoted characteristic radiative transitions in lanthanide emitters.
As no obvious molecular rotor structure exists in the R-Eu-Et-2 structure, its AIE properties may be derived from the rare RIV mechanism.In the unimolecular state, the cyclohexane moiety on the ligand R-L 2 in the R-Eu-Et-2 structure exhibits rapid free vibrations because of configuration changes, and the excited state energy returns to the ground state mainly through non-radiative transitions.In the aggregated state, the strong hydrogen bonding leads to the obvious restriction of the free vibration of the cyclohexane part in the R-Eu-Et-2 structure, and the non-radiative transition channel of the excited state energy is closed, thereby promoting the energy transfer process based on the antenna effect and opening the characteristic emission of Eu III ions.Thus far, lanthanide complex emitters are usually constructed by lanthanide metal ions and organic ligands.When a specific metal ion is selected, its luminescence mainly depends on the organic ligand with a specific connection and configuration 14 .Therefore, the luminescence performance of lanthanide complex emitters primarily depends on the complex ligand structure design, and achieving dynamic luminescence performance is challenging.Introducing molecular rotor structures or high-frequency vibration units into lanthanide complex emitters is an effective way to construct dynamic luminescent complexes with lanthanide emission.
In order to deeply explore the energy transfer pathway of R-Eu-Et-1/2, the Jablonski energy level diagram was further drawn (Fig. 4C).According to Reinhoudt's rule of thumb 21,48,49 , when the energy level difference between the excited singlet state and the excited triplet state of the ligand is greater than 5000 cm −1 , the intersystem crossing (ISC) process can be guaranteed to be effectived.At room temperature, (1 R/S,2 R/S)-(-/ + )−1,2-diphenylethylenediamine and (1 R/S,2 R/S)-(-/+)-cyclohexanediamine were stirred with 1-Ethyl-2imidazolecarboxaldehyde respectively, in 2 mL of CH 3 OH solution for 24 h to obtain R/S-L 1 and R/S-L 2 (Supplementary Fig. 29 and  Table 5).According to the solid-state UV-Vis absorption spectra of R-L 1 and R-L 2 , it can be seen that the energy values of the excited singlet states S 1 and S 1 ' of R-L 1 and R-L 2 are 27174 ( ± 95.42) and 28735 ( ± 105.1) cm −1 respectively (Supplementary Fig. 30A, B).Obviously, the lowest excited state energy level of Gd III ions (32500 cm −1 ) is significantly higher than the excited singlet energy levels of R-L 1 and R-L 2 , and energy cannot be transferred from the ligand to Gd III ions.Therefore, the phosphorescence spectrum of R-Gd-Et-1/2 was collected at 77 K, and the energy values of the excited triplet states T 1 and T 1 ' of R-L 1 and R-L 2 were obtained by Gaussian curve fitting to be 20025 ( ± 75.58) and 20566 ( ± 89.91) cm −1 , respectively (Supplementary Fig. 30C, D).The ΔE L between the excited singlet state and excited triplet state of R-L 1 and R-L 2 was calculated to be 7149 ( ± 19.84) and 8169 ( ± 15.19) cm −1 respectively.Obviously, the above ΔE L are all higher than 5000 cm −1 , indicating that R-L 1 and R-L 2 can effectively carry out the ISC process.The energy gap (ΔE) between the excited triplet energy level of the ligand and the lowest excited state energy level of Ln III must be in a suitable range for effective energy transfer process 50,51 .According to Latva's rule of thumb, a ΔE of 2000−5000 cm −1 is optimal for the energy transfer process of Eu III , while the optimal ΔE of energy transfer for Tb III ions is 2400 ± 300 cm −1 52-54 .In addition, the energy value of the 5 D 0 energy level of Eu III ions is 17500 cm −1 , and the energy value of the 5 D 4 energy level of Tb III is 20400 cm −1 .Further calculations show that the ΔE between the excited triplet states of R-L 1 and R-L 2 and the 5 D 0 of Eu III ions are 2525 ( ± 75.58) and 3066 ( ± 89.91) cm −1 respectively.Obviously, both R-L 1 and R-L 2 can efficiently sensitize the luminescence of Eu III ions.In addition, the ΔE between the excited triplet states of R-L 1 and R-L 2 and the 5 D 4 of Tb III ions are −375 ( ± 75.58) and 166 ( ± 89.91) cm −1 respectively, indicating that they are unable to transfer energy to Tb III ions through effective antenna effects (Fig. 4C).Density functional theory calculations (DFT; functional/ basis set are GGA-PBE/DND) were used to obtain the electron cloud distribution and the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) (Fig. 4D and Supplementary Data 3 and 4).Clearly, the main concentration of electron clouds on organic ligands demonstrates their great potential as antennas 55 .In addition, the electron cloud on the organic ligand obviously shifts to the metal center Eu III ions under excited state conditions.The absorption of polarized light by two pairs of enantiomers R/S-Eu-Et-1 and R/S-Eu-Et-2 in the aggregated state was measured using circular dichroism (CD) absorption spectroscopy.As shown in Fig. 4E, F, both R/S-Eu-Et-1 and R/S-Eu-Et-2 exhibit good mirror image CD curves in the aggregated state, indicating that the R/S-Eu-Et-1 and R/S-Eu-Et-2 are all enantiomers of each other.Furthermore, their Cotton effects at 265/264 nm (R/S-Eu-Et-1) and 294/ 315 nm (R/S-Eu-Et-2) may be attributed to the characteristic absorption of the diphenyl unit.Therefore, R/S-Eu-Et-1 and R/S-Eu-Et-2 in the aggregate state can show specific chiralities.
CD and luminescence are two key factors in the construction of CPL materials 56 .In addition, two key indicators to characterize the performance of CPL are g lum and B CPL (g lum = 2(I L − I R )/(I L + I R ), where I L and I R are the intensities of emitted left and right circularly polarized light, respectively).The CPL brightness is given by where ε λ is the molar absorptivity at the excitation wavelength and Φ is the QY 31 .However, high B CPL values can be obtained from strongly absorbing molecules with relatively low asymmetry factors, whereas unusually strong asymmetry factors are hampered by weak molar absorptivity and QY.Therefore, taking both g lum and B CPL into consideration and realizing their double promotion is challenging 31 .Lanthanide metal ions typically exhibit high g lum due to possible magnetic dipole-allowed transitions.In addition, the characteristic radiative transition of lanthanide emitters can be promoted by enhancing the antenna effect to obtain a high QY Φ.Therefore, lanthanide complexes are one of the best candidates for developing CPL materials.In particular, the Eu III complexes, whose 5 D 0 → 7 F 1 energy level has high g lum , have attracted extensive attention.Based on the CD and PL properties of R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2, we further tested the CPL performance of the above complexes.Both R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 dispersed in CH 3 CN solution exhibited distinct mirror image CPL signals (Fig. 4G, I, and Supplementary Fig. 31).Specifically, obvious mirror image CPL signal peaks were observed at 578, 606, 634, and 668 nm for R/S-Eu-Et-1, which were assigned to the 5 D 0 → 7 F 1 , 5 D 0 → 7 F 2 , 5 D 0 → 7 F 3 , and 5 D 0 → 7 F 4 energy level transitions of Eu III ions, respectively (Fig. 4G).According to g lum = 2(I L -I R )/(I L + I R ), the corresponding g lum values of R/S-Eu-Et-1 at 578, 606, 634, and 668 nm were calculated as 0.64/0.62,0.06/0.08,0.17/0.05and 0.17/0.18,respectively (Fig. 4H).According to B CPL = ε λ •Φ•|g lum | /2, the corresponding B CPL values of R/S-Eu-Et-1 at 578, 606, 634, and 668 nm were calculated as 2429/2353, 228/304, 645/190 and 645/683 M −1 cm −1 , respectively (Supplementary Table 6 and the absorbance of the corresponding molar absorptivity ε λ is obtained from Supplementary Fig. 32).Similarly, R/S-Eu-Me-1 exhibited obvious image CPL signal peaks at the same wavelength, which were attributed to the 5 D 0 → 7 F 1~4 energy level transition of Eu III ions (Supplementary Fig. 31A).The corresponding g lum values of R/S-Eu-Me-1 at 578, 606, 635, and 668 nm are 0.62/0.49,0.08/0.14,0.14/0.16,and 0.18/0.13,respectively (Supplementary Fig. 31B).The B CPL values were 2376/1813, 307/518, 536/592, and 690/ 481 M −1 cm −1 , respectively (Supplementary Table 6).Moreover, R/S-Eu-Et-2 also showed obvious mirror image CPL signal peaks at 580, 609, 635, and 671 nm, which can also be attributed to the 5 D 0 → 7 F 1~4 energy level of Eu III ions transition (Fig. 4I).The corresponding g lum values of R/S-Eu-Et-2 at 575, 619, 635, and 671 nm are 0.06/0.08,0.02/0.02,0.16/0.17and 0.05/0.05,respectively (Fig. 4J).The B CPL values were 121/150, 40/38, 321/320, and 100/94 M −1 cm −1 , respectively.Although the maximum B CPL value of chiral Eu III complexes is 3240 M −1 cm −1 , the B CPL of most chiral Eu III complexes is still less than 500 M −1 cm −1 (Supplementary Table 7).Therefore, R/S-Eu-Et-1 with a B CPL value of 2429/ 2353 M −1 cm −1 is at a high level.In summary, these chiral Eu III complex emitters (R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2) possess both high g lum and B CPL values (realizing the double improvement of the two), indicating good CPL performance, and suggesting great application prospects in the 3D optical display, biological imaging, chiral optoelectronic devices, and sensors.

Sensing properties of R-Eu-Et-1/2
Compared with high-nuclear lanthanide clusters or polymers (Ln-HOFs, Ln-MOFs, etc.), mononuclear lanthanide complexes have better dispersion and solution processability.Therefore, simple and cheap lanthanide mononuclear complexes are easier to process further and have higher application prospects in the fields of smart sensing, solidstate lighting, and multiple anti-counterfeiting 57 .On the basis of the structural characteristics and excellent luminescent properties of R-Eu-Et-1/2, the intelligent sensing of different heavy metal ions dispersed in CH 3 CN solution was further explored.Specifically, aqueous solutions containing different metal ions (such as Cu II , Co II , Fe III , Ag I , Ca II , Cd II , Ce III , K I , Mg II , Mn II , Nd III , Ni II , Pr III , Y III , and Zn II ) at the same concentration (20 μM) were added to acetonitrile solutions (3 mL) containing R-Eu-Et-1 or R-Eu-Et-2.Observe the luminescence change of the above mixed solution under a 365 nm UV-lamp.R-Eu-Et-1 or R-Eu-Et-2 without additional metal ions showed bright red luminescence.In addition, most of the solutions with added metal ions still maintained bright red luminescence (Fig. 5A, B).However, the red luminescence of R-Eu-Et-1 solutions containing Cu II , Co II , and Fe III ions was effectively quenched; the Cu II ions showed the best quenching effect, and the solution luminescence was almost completely lost (Fig. 5C).Similarly, the luminescence of R-Eu-Et-2 in solutions containing Cu II and Co II ions was effectively quenched (Fig. 5D).
Accordingly, we tested the response sensitivities of R-Eu-Et-1/2 dispersed in CH 3 CN solution to different contents of Cu II ions and calculated their limits of detection (LOD).Specifically, 0-6/12 μL of Cu II ion solution (20 μM) was accurately pipetted and added to the CH 3 CN solution containing 2 mL of R-Eu-Et-1/2, respectively, and observed the luminescence change of the above mixed solution under a 365 nm UVlamp.Solutions containing R-Eu-Et-1 or R-Eu-Et-2 exhibited characteristic emissions of Eu III ions ( 5 D 0 → 7 F 1 , 592 nm, 5 D 0 → 7 F 2 , 617 nm, 5 D 0 → 7 F 3 , 650 nm, and 5 D 0 → 7 F 4 , 685 nm) which gradually decreased with the continuous addition of Cu II ions, and were finally completely quenched (Fig. 5E, F).The red characteristic emissions of the R-Eu-Et-1/2 solutions were completely quenched when the added Cu II ion solution reached 6 and 9 μL, respectively.According to the Stern-Volmer equation (I 0 /I = 1 + K SV [M]), the detection limits for Cu II were calculated to be 2.55 and 4.44 nM, respectively, for the R-Eu-Et-1/2 solutions (Fig. 5G).Note that the detection limits of R-Eu-Et-1/2 for Cu II ions are much below the maximum approved concentration prescript by the USEPA, evidencing the great potential of R-Eu-Et-1/2 for the detection of trace amounts of the heavy metal ion Cu II in water.In addition, the UV-Vis absorption spectra of R-Eu-Et-1/2, R-Eu-Et-1 + Cu II , and R-Eu-Et-2 + Cu II were tested respectively, and the results showed that they all showed an obvious absorption peak with a wavelength of approximately 295 nm, which can be attributed to the characteristic absorption of organic ligands (Supplementary Fig. 33).It is worth noting that the above UV-Vis absorption peak does not have obvious characteristic absorption of Cu II ions, indicating that the concentration of Cu II ions in the sensing process is particularly low.We further explored the optical sensing sensitivity of Eu-Et-3 to Cu II ions (the experimental conditions are the same as R-Eu-Et-1/2).Cu II ions sensing experiments show that the detection limit of R-Eu-Et-1 with AIE behavior is much higher than that of Eu-Et-3 (LOD = 534.22nM), which is about 209 times (Supplementary Fig. 34).Therefore, the introduction of the molecular rotor or vibration unit strategy to construct lanthanide complexes with AIE behavior opens up a horizons for improving their optical, sensing and other properties.The capability of efficiently identifying the focal object in a complex environment is an essential feature of a sensor.R-Eu-Et-1 can efficiently respond to trace amounts of Cu II ions under the conditions of a variety of interfering ions, a feature which proves its reliability as an excellent sensor component (Supplementary Fig. 35).Compared with other Cu II ion sensors, such as ratiometric fluorescent probes (ZTM@FITC, 5.61 nM and 4.96 nM) 38 , polyacrylonitrile nanoparticles (tPAN NPs, 10 nM) 58 , inorganic-organic silica materials (SBA-P2, 6.5 nM) 59 , carbon dots (CD, 20 nM) 60 fluorescently active hybrid materials (SiO 2 @PBATPA, 85 nM and 184 nM) 61 , lanthanide-doped metal-organic frameworks (Eu@1, 10 nM) 62 , and our previously reported lanthanide hydrogen-bonded organic framework (TbZn-HOF, 1.91 nM) 14 , R-Eu-Et-1 and R-Eu-Et-2 have lower detection limits for Cu II , with excellent sensing performance (Fig. 5H).In addition, we also explored the optical response sensitivity of R-Eu-Et-1/2 in the aggregated state to Co II and Fe III ions respectively and obtained their detection limits.First, a Co II ion aqueous solution with a concentration of 0.46 mM was gradually added to the R-Eu-Et-1/2 solution, and it was observed that the characteristic emission of Eu III ions in the above solution gradually weakened and was eventually completely quenched.The LODs of R-Eu-Et-1/2 for Co II ions were calculated to be 53 and 32.8 nM, respectively (Supplementary Fig. 36).Similarly, with the continuous addition of Fe III ion aqueous solution with a concentration of 0.47 mM, the emission peak of R-Eu- Et-1/2 gradually weakened and was finally completely quenched.Further, the LODs of R-Eu-Et-1/2 for Fe III ions were 48 and 71 nM, respectively (Supplementary Fig. 37).The detection of low-concentration metal ions often mainly uses instruments such as inductively coupled plasma mass spectrometry and atomic absorption spectrometry.The above-mentioned detection process usually relies on bulky instruments, complex sampling procedures, and execution by professionals, making the entire detection process cumbersome, time-consuming, and costly.R-Eu-Et-1/2 with excellent optical properties is expected to be prepared into fluorescent test paper or a convenient identifier for optical sensing of specific metal ions with the help of anticounterfeiting ink technology.Simple optical sensing test strip technology can effectively avoid the cumbersome procedures and expensive costs of large-scale instrument testing.Target analytes can be detected with the naked eye only with the help of portable low-power UV-lamps.Therefore, R-Eu-Et-1/2 are expected to become a simple, economical, portable, and highly visible in vitro metal ion optical sensing test strip.
To explore the sensing mechanism of chiral mononuclear Eu III complexes R-Eu-Et-1/2 to heavy metal ion Cu II , the R-Eu-Et-1 solution before and after adding Cu II ions was subjected to HRESI-MS.In the positive ion mode, the key molecular ion peaks in the R-Eu-Et-1 solution without adding Cu II ions were [Eu(R-L 1 )(NO 3 ) 2 ] + (m/z = 701.13 3) and [Eu 2 (R-L 1 ) 2 (NO 3 ) 5 ] + (m/z = 1426.26)(4) (Fig. 5I and Supplementary Fig. 38).The main molecular ion peaks in the R-Eu-Et-1 solution after adding Cu II ions were [Cu(R-L 1 )] + (m/z = 487.16)(5), and [Cu(R-L 1 )(NO 3 )] + (m/z = 549.15)(6) (Fig. 5I and Supplementary Fig. 38).The above HRESI-MS results indicate that Cu II ions can replace Eu III ions in the chiral Eu III complex structure, leading to strong LMCT to achieve luminescence quenching (Fig. 5J).In conclusion, both chiral mononuclear Eu III complexes R-Eu-Et-1/2 exhibit excellent dynamic optical sensing properties for trace amounts of Cu II ions, opening up-to-date horizons for the development of ultra-efficient and sensors for heavy metal ions.
With rapid industrial development, the amount of acid/alkaline wastewater has increased swiftly.Such wastewater contains various harmful substances or heavy metal salts, which is highly corrosive, has seriously threatened human health, and caused irreversible damage to the ecology.Therefore, the development of sensors that accurately monitor pH is of great significance to various research fields ranging from the environment to chemical biology 63 .In recent years, lanthanide complex emitters have been widely used in chemical sensing, such as the detection of explosives, heavy metal ions, and small organic molecules 7,8 .However, the progress of lanthanide complex emitters for efficient light-responsive pH sensors still lags.Therefore, constructing optical sensors of lanthanide complexes with smart photo-responsiveness in a narrow pH range for precise measurement of acidic and basic pH values remains extremely challenging.Based on the aforementioned work and background, we explored the photoresponse behavior of chiral Eu III complexes R-Eu-Et-1/2 in a specific pH range.Specifically, 0-110 μL of the aqueous solution of C (H + ) = 0.001 molL −1 (pH = 3) was accurately pipetted into the CH 3 CN solution containing R-Eu-Et-1/2 (2 mL), respectively, and the luminescence changes of the above mixed solutions were observed under the irradiation of a 365 nm UV-light.Solutions containing both R-Eu-Et-1/2 showed efficient and clear characteristic emission of Eu III ions ( 5 D 0 → 7 F 1 , 592 nm, 5 D 0 → 7 F 2 , 617 nm, 5 D 0 → 7 F 3 , 650 nm, and 5 D 0 → 7 F 4 , 685 nm).With the continuous addition of pH = 3 acidic aqueous solution, the characteristic emission peak intensity of the chiral lanthanide complexes gradually decreased (Fig. 6A, D).Similarly, accurately pipetted 0-55/65 μL of C (OH − ) = 0.01 molL −1 (pH = 12) aqueous solution was introduced into the acetonitrile solution (2 mL) containing R-Eu-Et-1/2, and observed the luminescence change of the above mixed solution under the irradiation of 365 nm UV-light.Both solutions containing R-Eu-Et-1/2 showed the characteristic emission of Eu III ions, and the intensity of the above emission peaks gradually decreased with the continuous addition of pH = 12 aqueous solutions (Fig. 6B, E).The red characteristic emission of R-Eu-Et-1/2 solutions was completely quenched when the added acid or alkaline solution reached 110 and 55/65 μL, respectively.Note that both chiral Eu III complexes R-Eu-Et-1/2 achieved a linear decrease in emission in the ranges of pH = 4.28-6.) ) (Fig. 6C, F).Compared with the reported fluorescent pH sensors (example: Zn-MOF, pH = 4-11 64 , Zr-MOF, pH = 4.6-7.12 65, NGQDs, pH = 1.8-13.5 66 , Tb-NCs, pH = 3-10 67 , Tb-MOF, pH = 2-7 68 , and Lum-MDI-CA/MTPP, pH = 1-2 and 12-14 63 ), R-Eu-Et-1/2 can intelligently photoresponse to acidic and alkaline solutions in a narrower pH range, and the response process shows a linear change, achieving excellent pH sensing behavior (Fig. 6G).As far as we know, this work is a rare example of the application of chiral lanthanide complex emitters to sensing of low-concentration acidic or alkaline solutions, which provides a strategy for the development of photoresponsive pH sensors with high sensitivity.In addition, the optical response sensitivities of R-Eu-Et-1/2 to Cu II ions under different pH conditions were explored, and their LODs were obtained.Specifically, Cu II ion aqueous solutions under acidic or alkaline conditions (pH = 4, 5, 6, 9, 10, and 11) were gradually added to solution R-Eu-Et-1 or R-Eu-Et-2 respectively, and it was observed that the characteristic emission of Eu III ions of the above solutions gradually weakened and was eventually completely quenched.Through calculation, the LODs of R-Eu-Et-1/2 for Cu II ions under different pH conditions are 0.081 and 0.65 nM (pH = 4), 0.086 and 0.64 nM (pH = 5), 0.1 and 0.99 nM (pH = 6), 0.11 and 0.86 nM (pH = 9), 0.1 and 0.98 nM (pH = 10), 0.12 and 0.85 nM (pH = 11) (Supplementary Fig. 39, 40).The above experimental results prove that R-Eu-Et-1/2 can be used to sense trace amounts of heavy metal ions Cu II ions under different pH conditions, showing great potential for specific sensing of Cu II ions in complex environmental pollutants.

Double anti-counterfeiting performance of R-Eu-Et-1/2
With the rapid development of fluorescent materials, anticounterfeiting technology is also constantly innovating.Among such technology, anti-counterfeiting fluorescent materials used in photoluminescent printing have shown great application prospects in the field of anti-counterfeiting given their low cost, simple design, and environmental protection 24,69 .The efficient and fast response behavior of R-Eu-Et-1/2 to the aqueous solution with low concentration (trace amount) of Cu II ions further expands their application in double anticounterfeiting.Specifically, we dispersed R-Eu-Et-1/2 in an aqueous solution with polyethylene glycol and sonicated the mixture to make a simple ink which was then evenly spread on ordinary filter paper with patterns and numbers.Under a daylight lamp, only black and white peony flower patterns and the number 8 can be seen, but under the condition of 365 nm UV-light, the peony flower pattern and the number 8 can be seen with the eye by emitting strong red light (Fig. 7).Note that when the Cu II ion aqueous solution with a concentration of only 6 μM is sprayed on the center of the peony flower and a part of the number 8, the obvious red luminescence can be quickly observed to be completely quenched, which shows the fast and efficient anticounterfeiting characteristics.

Discussion
We carefully designed and selected chiral ligands with the molecular rotor or vibrating element structures, and constructed three pairs of dynamic chiral Eu III complex emitters with AIE behavior through the RIR or RIV mechanism in the induced aggregation state R/S-Eu-R-1 and R/S-Eu-R-2 (1, R = Et/Me; 2, R = Et).R/S-Eu-R-1 and R/S-Eu-R-2 in the molecular state have no obvious luminescence behaviors and exhibit the obvious characteristic emission of Eu III ions; moreover, the emission of such ions increases rapidly with the increase of the aggregation degree.In the molecular state of R/S-Eu-R-1 and R/S-Eu-Et-2, the molecular rotors or vibrational elements in the structure dissipate the energy of the excited state through non-radiative transitions.In the aggregated state, the movement of the rotors or vibrational elements is restricted, leading to the opening of the ISC process.Further, the aggregation-promoted antenna effect is realized to obtain bright emission.In addition, both R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2 showed excellent CPL performances, with the g lum of R-Eu-Et-1 as high as 0.64 ( 5 D 0 → 7 F 1 ) and the B CPL as high as 2429 M −1 cm −1 , achieving a rare double increase in the g lum and B CPL values.The construction of organic ligands based on RIR and RIV properties usually requires complex operations and low-yield organic synthesis.We used a simple and efficient solvothermal one-pot method to obtain R/S-Eu-R-1 (R = Et/Me) and R/S-Eu-Et-2, thereby opening a door for the construction of dynamic chiral lanthanide complex emitters.The metal center Eu III of R-Eu-Et-1/2 with bright emission can be replaced by the heavy metal ion Cu II , showing a fast and selective photoresponse to trace Cu II ions, and their LODs were as low as 2.55 and 4.44 nM, significantly outperforming the other types of luminescent materials.In addition, R-Eu-Et-1 can selectively photoresponse to acidic or basic aqueous solutions in a narrow pH range, showing a rare high sensitivity to low-content acidic and basic solutions.Finally, this work introduces chiral molecular rotors or vibrational units to provide vivid examples of the construction of dynamic chiral lanthanide complexes with bright emission.These chiral Eu III complexes have high CPL parameters and sensing properties, opening a horizon for the construction of multifunctional chiral lanthanide complex emitters.

Fig. 2 |
Fig. 2 | Structural analysis.A, E Molecular structures of R-Eu-R-1 (R = Et/Me) and R-Eu-Et-2.B, F Schematic diagram of the free rotation/vibration restriction of the benzene ring/cyclohexane of R-Eu-Et-1/2 in the aggregated state.C, G Hydrogen bonding of R-Eu-Et-1/2.D, H Topological structure of R-Eu-Et-1/2.Note: The blue and yellow arrows represent the rotation/vibration of the molecular rotor.

Fig. 3 |
Fig. 3 | Characterization of AIE properties.A, D, G, J Emission spectra of R/S-Eu-Et-1 and R/S-Eu-Et-2 in different contents of glycerin/DMSO mixed solutions under excitation at 365 nm, the inset shows the luminescence photos of R/S-Eu-Et-1 and R/S-Eu-Et-2 in 0 and 99% glycerin/DMSO mixed solutions respectively under UVlight.B, E, H, K Luminescence intensities of R/S-Eu-Et-1 and R/S-Eu-Et-2 at 617 nm as a function of f w , the inset shows the photoluminescence of R/S-Eu-Et-1 and R/S-Eu-Et-2 in different proportions of glycerin/DMSO mixed solutions under UV-light.C, F, I, L Absorption spectra of R/S-Eu-Et-1 and R/S-Eu-Et-2 in glycerin/DMSO mixed solutions with different contents of f w , the insets show the DLS results of R/S-Eu-Et-1 and R/S-Eu-Et-2 in 99% glycerin/DMSO mixture.Note: The orange dotted circle represents the luminous intensity position of R/S-Eu-Et-1 and R/S-Eu-Et-2 under the condition of mixed solution (99% glycerin: 1% DMSO): (0% glycerin: 100% DMSO); f w represents the ratio of glycerin to DMSO.

Fig. 4 |
Fig. 4 | Photophysical properties and theoretical calculations.A Solid-state luminescence spectrum under excitation at 365 nm (D represents the quintet; F represents the septet).B The decay curve of 5 D 0 energy level in solid-state R-Eu-Et-1/2.C Schematic diagram of the Jablonski energy levels in different states.D The electron cloud density maps of R-Eu-Et-1/2 by DFT theoretical calculation (GGA-PBE/DND).E, F CD spectra of R/S-Eu-Et-1 and R/S-Eu-Et-2 dispersed in CH 3 CN solution.G, I CPL and DC spectra.H, J corresponding g lum values.Note: The green and yellow balls represent excitons; Abs.Absorption, FL fluorescence, Phos.Phosphorescence, ISC intersystem crossing, ET energy transfer.

Fig. 5 |
Fig. 5 | Study on the sensing performance.A, B Under 365 nm excitation, emission spectra of R-Eu-Et-1/2.C, D Luminescence intensity comparison of R-Eu-Et-1/2 solutions after adding different metal ions (insets in C, D: photos of R-Eu-Et-1/2 photoresponses to different metal ions under 365 nm UV-light).Concentrationdependent spectra and fitting curves of R-Eu-Et-1/2 on Cu II ions under excitation at 365 nm (E and G for R-Eu-Et-1, F, and G for R-Eu-Et-2).H Performance comparison of R-Eu-Et-1/2 and different types of materials reported for Cu II ion sensing.I Molecular ion peaks and analytical results of the HRESI-MS of R-Eu-Et-1 before and after adding Cu II ions.J Schematic diagram of the photoresponses of R-Eu-Et-1 or R-Eu-Et-2 to heavy metal ion Cu II .Note: The yellow ball represents the series of hydrogen bonds/metal-organic framework; the pink ball represents the series of quantum dots; the purple ball represents the series of nanoparticles; the red star represents this work; The shade of red represents the glow color of R-Eu-Et-1 or R-Eu-Et-2.

Fig. 6 |
Fig. 6 | Sensing experiment of acid and alkali solutions.R-Eu-Et-1 to C (H + ) = 0.001 M (pH = 3) (A) and C (OH − ) = 0.01 M (pH = 12) (B) concentrationdependent PL spectra under excitation at 365 nm and fitting curves of aqueous solutions (C).E, F R-Eu-Et-2 to C (H + ) = 0.001 M (D) and C (OH − ) = 0.01 M (E) concentration-dependent PL spectra under excitation at 365 nm and fitting curves of aqueous solutions (F).G Comparison of the pH ranges of R-Eu-Et-1/2 and different types of pH sensors that have been reported.Note: Dark blue shading represents a series of metal-organic frameworks; orange shading represents quantum dots; green shading represents a series of nanoparticles; yellow shading represents small molecules; light blue shading represents this work.

Fig. 7 |
Fig. 7 | Anti-counterfeiting performance.Patterns of peony flowers and the number 8 drawn by anti-counterfeit inks containing R-Eu-Et-1 (A, B) and R-Eu-Et-2 (C) under a daylight lamp and at 365 nm and after spraying the Cu II ion solution security pattern.